Fluid Bypass Device for Valved Catheters

ABSTRACT

Bypass elements for medical valves and methods of using the same are disclosed. Embodiments of the invention include an insert having a tip that is adapted to displace a valve element without penetrating it, and a lumen that fluidly communicates with a lumen of a valve housing distal to the valve element when the bypass element is engaged. Bypass elements are used, in certain embodiments, to facilitate fluid pressure and ECG signal measurements through implanted medical devices including catheters.

TECHNICAL FIELD

The present invention relates to systems and methods for transmission and measurement of fluid through valved catheters.

BACKGROUND

There are a number of implantable medical devices used for the repeated and prolonged access to a patient's vascular system or other bodily conduits. Such devices include peripherally-inserted central catheters (“PICC's”), central venous catheters (“CVC's”), dialysis catheters, implantable ports, and midline infusion catheters. These devices are typically implanted into a patient for an extended period of time to allow for multiple treatments, such as the delivery of therapeutic agents or dialysis treatments. Use of such devices eliminates the need for multiple placements of single-use devices, thus reducing the risk of infection and placement complications, and reducing the overall cost of patient care. Examples of such implantable medical devices include BioFlo™ PICC's, Vaxcel® PICC's, Xcela® PICC's, and Vaxcel® Plus Chronic Dialysis catheters (all from AngioDynamics, Inc., Latham, N.Y.). Implantable devices such as these have distal sections that reside within the vasculature, and proximal sections that are typically outdwelling and include luers for connection to fluid sources and other medical devices.

Because these devices remain in a patient's body for an extended period of time, it is common practice to seal their proximal ends between uses to prevent blood loss and infection. Such a seal may be created with the use of a simple clamp placed on the catheter line (e.g. the Morpheus® SMART PICC, AngioDynamics, Inc., Latham, N.Y.), or with the use of an in-line valve such as that found in the Vaxcel® PICC with PASV® Valve Technology and described in U.S. Pat. Nos. 5,205,834 and 7,252,652, which are incorporated herein by reference. In-line valves are pressure activated such that they open to allow for fluid to be delivered through the valve upon the application of some threshold pressure, above which the valve will open, and below which the valve remains closed. Pressure activated valves may advantageously prevent patient complications and infections. In line catheter valves typically include a valve housing that defines a lumen (referred to as the “valve lumen”) and a valve element disposed across the valve lumen to regulate fluid flow. The valve element is normally closed, but opens in response to pressures above a pre-defined threshold. Valve elements used in in-line catheter valves are typically flexible slitted membranes such as those disclosed in U.S. Pat. No. 5,843,044, which is incorporated by reference herein.

It is often desirable to measure fluid pressures such as blood pressure or central venous pressure through a catheter. It may also be desirable to measure an ECG signal through a column of saline extending from a distal catheter tip to a proximal extension tube and luer. In the case of valved devices, however, the in-line valve inhibits transmission of fluid pressure from the distal catheter tip to the proximal luer. Current practice is to insert an elongated instrument through the valve element (typically a slitted membrane), but the insertion of elongated tools into the valve lumen to measure blood pressure raises a risk of puncturing the membrane or tearing, weakening, or otherwise permanently deforming the membrane or its slits. Additionally, excessive displacement of the edges of slit raises the risk that the edges will not return to their fully closed, fully and flushly apposed positions, instead returning to a folded or puckered position, and that gaps or edges may exist through which fluids may leak, potentially leading to thrombosis and/or infection. Accordingly, there is a need for systems that permit the measurement of blood pressure through catheters having in-line valves, preferably without the risk of damaging the valve element.

SUMMARY OF THE INVENTION

The need described above is met by the present invention, which relates in one aspect to a bypass element for a valve which opens but does not penetrate the valve element, permitting fluid communication across the valve element. In certain embodiments, the insert includes an insert tip that displaces one or more edges of a slit in a membrane without penetrating the slit, as well as an insert connector connectable to a measurement device, which is in fluid communication with the insert tip via an insert lumen that permits fluid flow between the insert tip and the insert connector. The insert may have an outer diameter sized to fit within the valve lumen. In various embodiments, the insert is longitudinally compressible by means of a distal portion that includes the insert tip, a proximal portion that includes the connector, and a compressible element disposed at a junction of the proximal and distal portions. The proximal and distal portions can optionally rotate relative to one another, and the insert optionally includes a sealing member disposed at the junction of the proximal and distal portions to prevent leakage into or out of the insert lumen at the junction of the proximal and distal insert portions.

In another aspect, the invention relates to a system for measurement that includes a catheter insertable into a patient, including a valve housing with a valve lumen and a flexible slitted membrane positioned in the valve lumen which membrane remains closed under pressures below a threshold value, and an insert that includes an insert section that fits inside the valve lumen and opens the slit, as well as a proximal connector that can be engaged with the catheter and an insert lumen that runs between the insert tip and the insert connector and permits fluid flow between them. In certain embodiments the insert is longitudinally compressible by means of a distal portion that includes the insert tip, a proximal portion that includes the connector, and a compressible element disposed at a junction of the proximal and distal portions. The proximal and distal portions can optionally rotate relative to one another, and the insert optionally includes a sealing member to prevent leakage into or out of the insert lumen at the junction of the proximal and distal portions.

In yet another aspect, the invention relates to a method of measuring a physical characteristic in a patient with a catheter having a pressure activated valve that, in turn, utilizes a membrane with at least one slit, which slit opens in response to a fluid pressure in excess of a predetermined threshold, as a valve element. The method includes, in various embodiments, providing an insert that has a section which fits inside the valve lumen, contacts the membrane and opens the slit without penetrating it, as well as a proximal connector that can be engaged with the catheter and an insert lumen that runs between the insert tip and the insert connector and permits fluid flow between them. The method also includes placing the insert into the valve housing to permit fluid transmission between the catheter and the insert lumen through the open slit. The physical characteristic may be selected from the group consisting of pressure waves, acoustic waves and ECG waves, and the method may also include one or more of the steps of determining the position of the distal tip of the catheter based on the measured wave, and optionally repositioning the distal tip of the catheter based on the measurements to achieve targeted tip position. The method may also include positioning the distal tip of the catheter in an optimal position during initial insertion of the catheter.

DESCRIPTION OF THE DRAWINGS

The figures provided herein are not necessarily drawn to scale, with emphasis being placed on illustration of the principles of the invention.

FIGS. 1A-1B include schematic depictions of an insert and a pressure activated valve in accordance with certain embodiments of the invention.

FIGS. 2A-2B include schematic depictions of an insert positioned within a pressure activated valve in accordance with certain embodiments of the invention.

FIGS. 3A-3D include schematic depictions of valve inserts in perspective and in cross-section according to certain embodiments of the invention.

FIGS. 4A-4F include schematic depictions of valve inserts in isolation or positioned within pressure activated valves according to certain embodiments of the invention.

FIGS. 5A-5C include schematic depictions of various relationships between valve inserts and valves of the invention, as well as a schematic depiction of a prior art device.

FIGS. 6A-6B include schematic depictions of an insert having an extension tube according to certain embodiments of the invention.

FIGS. 7A-7B include schematic depictions of inserts having branching insert lumens according to certain embodiments of the invention.

DETAILED DESCRIPTION

Devices and methods to facilitate fluid transmission through valved catheters are disclosed herein. Although physical characteristics of a human body can be measured using elongated tools inserted through valved catheters, this approach risks damaging in-line catheter valves. The systems and methods described herein avoid the risk of valve damage by using an insert that displaces but does not penetrate a valve element.

Examples of medical devices that can be used with the invention include, without limitation, peripherally-inserted central catheters (“PICC's”), central venous catheters (“CVC's”), dialysis catheters and midline infusion catheters that include internal valves. While the examples set forth in this specification focus on implantable catheters for vascular access, the systems and methods of the invention are not limited to vascular devices but are compatible with any medical device having an external valve, including diagnostic and/or interventional catheters and sheaths Similarly, while the examples set forth herein focus on valves having a flexible diaphragm with one or more slits, the principles of the invention are compatible with a variety of normally-closed pressure activated valve designs.

With reference to the embodiments depicted in FIG. 1, a system 100 according to the invention includes a valve housing 150. The valve housing 150 includes a valve inlet 151, a valve outlet 152, a proximal valve lumen 153 and a distal valve lumen 154. The proximal and distal lumens 153, 154 are separated by a valve element 155 which, in preferred embodiments, is a flexible membrane having at least one slit 156 therethrough. During ordinary valve operation, the edges of the slit 156 remain together, and fluid does not flow, unless a pressure differential thereacross exceeds a predetermined threshold. When a pressure differential across the valve element 155 exceeds the threshold, the membrane deforms so that the edges of the slit 156 separate and fluid flows across the valve from the side with higher pressure to the side with lower pressure.

The system 100 also includes an insert 200, which has a distal insert section 210, a proximal insert end 211, an insert shaft 220, and an insert lumen 260 which extends from the distal insert tip 210 to the proximal insert end 211 and is open to the exterior of the insert in both places. In preferred embodiments, the insert 200 also includes a proximal connector 240 that can be attached to a pressure measurement and/or pressure transduction apparatus, and a proximal external housing 230 that can connect to the valve inlet 151 of the valve housing. Insert shaft 220 is sized to fit within the proximal valve lumen 153 of the valve housing 150. Thus, insert shaft 220 preferably has a maximum outer diameter that is slightly less than a minimum inner diameter of proximal lumen 153. As shown in FIG. 1A, the length 250 of insert shaft 220 preferably corresponds to the length 157 of the proximal valve lumen 153, so that when insert 200 is fully engaged with valve housing 150, as shown in FIGS. 1B and 2B, the distal insert tip 210 of the insert 200 contacts valve element 155 and displaces the flexible membrane it so that the edges of the slit 156 separate from one another. In use, the insert 200 preferably does not penetrate the valve element 155.

In some embodiments, after the insert 200 has been fully engaged with the valve housing 150, the insert lumen 260 is aligned with a gap between edges of the slit 156 so that fluid can flow and pressure can be directly transmitted between the insert lumen 260 and the distal valve lumen 154. As shown in FIG. 2, the opening of the insert lumen 260 at the distal insert tip 210 may be positioned so that, as the insert 200 is inserted into the proximal valve lumen 153 and the distal insert tip 210 approaches the membrane 155, the insert lumen 260 aligns with the slit 156 as shown in FIG. 2A. When the insert 200 is fully engaged with the valve 100, the distal insert tip 210 of the insert presses into the valve element 155, displacing the edges of the slit 156 and creating a fluid communication channel or gap 156′ through which fluid can flow between the insert lumen 260 and the distal valve lumen 154.

In some embodiments, however, the opening of the insert lumen 260 is not aligned with the slit 156, and either one or both of the opening of the insert lumen 260 and the slit 156 is offset from the central longitudinal axis of the insert 200 and/or the proximal and distal valve lumens 153, 154. In these embodiments, the distal insert tip 210 presses into the valve element 155, advantageously utilizing the elasticity of the membrane comprising the valve element to stretch and open the slit or slits 156, thereby permitting fluid flow and transmission of fluid pressure across the valve element 155 and between the proximal and distal lumens 153, 154. This in turn permits fluid flow and transmission of fluid pressure between the insert lumen 260 and the distal valve lumen 154.

With respect to the insertion of insert 200 into valve housing 150, in preferred embodiments, the insert 200 contacts the valve element 155, but does not penetrate the slit 156. As shown in FIGS. 5A and 5B, the at least one slit 156 has proximal edges 156P which face the proximal valve lumen 153 when the valve element 155 is closed, and distal edges 156D which faces the distal valve lumen 154 when the valve is closed. FIG. 5A shows an insert 200 of the invention positioned in so that it contacts valve element 155 but does not open the slit 156. When the valve is completely closed, the entire distal surface of the valve element 155 is disposed along the plane identified by reference line L₁. As the insert 200 is advanced in the valve housing 150, the distal insert tip 210 displaces the edges of the slit 156 downward and outward, such that the distal edge 156D of the slit 156 extend below reference line L₁. According to one embodiment, the inert is advanced no further than the position shown in FIG. 5C: the edges of the slit 156 are pressed apart, but at all times the proximal edges 156P remain proximal to the distal edges 156D of the slit 156 extend below reference line L₁. Preferably, the insert is advanced no further than the position shown in FIG. 5B. The edges of the slit 156 are pressed apart, but the proximal edges 156P preferably do not extend beyond the plane defined by reference line L₁, and remain proximal to the distal edges 156D, thereby minimizing the risk of leakage due to imperfect resealing and/or damage to the valve.

Inserts of the invention advantageously reduce the risk of leakage due to imperfect resealing and/or valve damage relative to devices disclosed in the prior art, such as the device 340 illustrated in FIG. 5C, in which an elongate member is inserted into and through the slit 156. In the prior art device, the edges of the slit 156 compress against the elongate member 340 and bulge into distorted portions 157P and 156D. Compression and distortion of the edges of the slit 156 in this manner increases the risks of imperfect re-sealing and permanent damage to the valve element.

In some embodiments, the insert 200 includes features to prevent the distal insert tip 200 from advancing too far. For example, the proximal insert connector 240 may include a female luer tip having a threading pattern selected so that, when the proximal insert connector is fully screwed down, it does not extend beyond the position shown in FIG. 5B.

FIG. 3 depicts an insert 200 according to two embodiments of the invention. The embodiment in FIG. 3A-B corresponds to a one-piece valve insert substantially as described above. In the embodiment of FIG. 3C-D, the valve insert 200 includes proximal and distal shafts 221, 222. A spring 270 or, in some embodiments, an elastomeric member is positioned around the junction of the proximal and distal shafts 221, 222, allowing for limited compression and extension of the valve insert about its long axis. The spring 270 preferably has a spring constant that is greater than or equal to that of the flexible membrane comprising the valve element 155 and is chosen to permit the distal insert tip 210 to apply sufficient force to displace the valve element 155 and separate the edges of the slit 156, but not enough to permit the distal insert tip 210 to penetrate the valve element 155. The combined length 250 of the proximal and distal shafts 221, 222 varies depending on the degree of compression, with the length 250 being slightly longer than the length 157 of the proximal valve lumen 153 when the valve insert 200 is not engaged with the valve housing 150, and compressing to fit within the proximal valve lumen 153 when engaged. In certain embodiments, the proximal and distal shafts 221, 222 can be rotated relative to one another. Thus, in embodiments in which the proximal external housing 230 of the valve insert 200 rotates to fit over the exterior of the valve inlet 151—for example if the valve inlet 151 includes a male luer end and the proximal external housing 230 includes a female luer end—the proximal shaft 221 can rotate freely with the proximal external housing 230 without translating that rotation to the distal insert tip 210 or the flexible membrane.

To prevent fluid leakage out of the insert lumen 210 at the junction of the proximal and distal shafts 221, 222, one or more compressible sealing members 280, 281 may be utilized as shown in FIG. 3C. Sealing members 280, 281 can be, for example, elastomeric O-rings or any other suitable sealing mechanism known in the art. The sealing member(s) may comprise any suitable material known in the art, including silicone, EPDM, polyurethane, neoprene, FEP, etc. In addition, the insert 200 may be configured to prevent leakage of fluid through the proximal valve lumen 153. In some embodiments, an outer diameter of a portion of the insert 200 which is inserted into the proximal valve lumen 153 is slightly less than the inner diameter of the proximal valve lumen 153, inhibiting or preventing fluid flow around the insert 200. In some embodiments, the proximal external housing 230 of the insert engages with the valve inlet 151 to form a seal that prevents fluid leakage out of the proximal valve lumen 153. In some embodiments, the insert 200 may have an outer diameter chosen to match up with an inner diameter of the lumen, possibly preventing leakage.

The shape of the distal insert tip 210 is chosen to facilitate proper function of the insert 200 while avoiding damaging the valve element 155. In preferred embodiments, such as the one shown in FIGS. 1-3, the distal tip is gently rounded. In alternate embodiments, the valve has a conical distal insert tip 210, as is shown in FIG. 4A-C, or a stepped distal insert tip 210, as is shown in FIG. 4D-F. The principle of operation remains the same regardless of the tip shape: when the valve insert 200 is fully engaged with the valve housing 150, as shown in FIGS. 4C and F, the tip 210 displaces but does not penetrate the valve element 155 so that the edges of the slit 156 separate, and the insert lumen 260 of the valve insert 200 is placed into fluid communication with the distal valve lumen 154. The insert lumen 260 may open at the distal insert tip 210 in any suitable configuration. In some embodiments, the opening of the insert lumen 260 at the distal insert tip 210 is circular, while in other embodiments, the opening is rectangular, oval shaped, or otherwise generally elongated so as to overlie a slit 156 of the valve element 155, which arrangement may improve fluid flow and transmission of pressures and/or prevent or minimize leakage around the distal insert tip 210. The internal threading 230 and the external threading 151 can be configured to align the rectangular or oval opening along the same lateral axis as the slit.

In some embodiments, the insert 200 facilitates the transmission and/or measurement of a pressure such as a central venous pressure, a V-pressure wave generated by the filling of the right atrium, an A-pressure wave generated by the contraction of the right atrium, or any other pressure caused, directly or indirectly, by a contraction of the heart of a patient which may be desired to be measured. The insert 200 can also facilitate the transmission and/or measurement of acoustic pressure waves such as those caused by the opening and closing of one or more cardiac valves, or acoustic waves caused by an external acoustic generator.

In some embodiments, the insert 200 facilitates the accurate placement of a distal end of a catheter, for example as disclosed in U.S. patent application Ser. No. 12/594,869 by David Ziv, published as Pre-Issue Publication number 2010/0049062, the entire disclosure of which is hereby incorporated by reference for all purposes. Using inserts of the invention, a distal end of a catheter may be located within the vasculature of a patient and/or may be placed in an optimal position for a given application. Positioning of a catheter may be achieved, for example, by measuring a delay time, phase shift, or amplitude of a pressure wave and/or an acoustic wave (or any other wave or signal) transmitted through a catheter and an insert of the invention and/or comparing the measured value to a reference value. More generally, inserts of the invention may be used to facilitate any treatment that includes the measurement of a signal or a substance that is transmitted through the valve of a catheter.

Using inserts of the invention, a catheter may be positioned during an insertion procedure at a desired site. Additionally, inserts of the invention may facilitate the repositioning of catheter tips that have migrated from their initial positions, or which need to be repositioned for other reasons.

Inserts of the invention may be configured to connect to a pressure measurement apparatus, such as a manometer apparatus or a digital pressure transducer system. In certain embodiments, the proximal insert connector 240 comprises a female luer tip that can be connected to and disconnected from a pressure measurement apparatus. In other embodiments, any suitable connector known in the art, including without limitation a threaded or unthreaded male or female luer connector or a barb connector, can be used to facilitate connections to a pressure measurement apparatus. The connections can be either reversible or permanent.

Alternatively, inserts of the invention may include features to facilitate direct pressure sensing, such as an electronic pressure transducer for sensing a fluid pressure within the insert lumen 260, a wire for conducting electrical signals generated by the electronic pressure transducer to a central processor, and/or an external valve for removing air from the fluid flow path that includes the insert 200 and the valve housing 150.

Valve inserts of the invention can be used in any application where it is desirable to measure a physical characteristic or signal from a patient across a valve member in a catheter. Valve inserts of the present invention are advantageously used to facilitate measurement of fluid pressure with a valved medical device. In a preferred embodiment, partially illustrated in FIG. 1, an insert 200 is inserted into a valve housing 150 so that the proximal external housing 230 connects to the valve inlet 151 of the valve housing 150 while the distal insert tip 210 engages with the valve element 155 and displaces the edges of the slit 156, placing the lumen 260 of the valve insert 200 in fluid communication with the distal valve lumen 154 of the valve housing 150. In certain embodiments, before insertion into valve housing 150, the valve insert 200 is connected via the proximal connector 240, directly to a pressure measurement apparatus, or to a tube that is connected to a pressure measurement apparatus. A directional stopcock or other fluid control device can also optionally be connected between the insert 200 and the pressure measurement apparatus. After the proximal connector 240 is connected to the pressure measurement apparatus, the entire system is optionally flushed with a fluid solution, so that no air is introduced into the system when the valve insert 200 is inserted into the valve housing 150. After the insert 200 is fully engaged with the valve housing 150, fluid can flow freely and pressure can be equalized through the entire system 100. To verify that the valve insert 200 is correctly inserted, an operator can push fluid through the system, or withdraw fluid from the system 100 and confirm that there is no resistance to fluid flow. An operator can also push or withdraw fluid through the system to purge any air from the system. Pressure measurements can then be taken through system 100.

Another application for valve inserts according to the invention includes transmission of fluid across a normally closed valve for ECG measurement via a column of saline or other transmission fluid. It is common to measure ECG signals from the heart for various clinical applications, such as detection of atrial fibrillation or ECG based tip location. The column of saline runs from the tip of the catheter, such as a PICC line, through to a proximal portion of the catheter, where the ECG signal is measured. The valve insert can be used to bypass the valve using the methods described above, so that the column of saline can be in fluid communication with the proximal ECG measurement element. In addition, the bypass element can itself have an incorporated ECG measurement element, such as an electrode connected to an inner valve insert wall in fluid communication with the lumen, or an electrode connected to a valve insert extension tube or luer.

Valve inserts of the invention can be made using any suitable method known in the art, including without limitation injection molding, extrusion, machining and combinations thereof. Valve inserts of the invention can be made of any suitable material known in the art, including without limitation polycarbonate, nylon, Pelox, polyethylene, polypropylene, FEP, ABS, metals including stainless steel, and other suitable materials, which may be combined in any suitable way. In some embodiments, at least a portion of the insert 200 that includes the tip 210 is made of stainless steel or another suitable metal.

In some embodiments such as those depicted in FIG. 6, the insert includes an extension tube 290, which can be clamped using a clamp 295 in order to prevent flow through the extension tube 290, thereby preventing fluid leakage through the insert 200, for example during insertion into the valve housing 150. In use, insert 200 is inserted into a valve housing 150 with the extension tube 290 clamped shut (FIG. 6B) in order to prevent reflux of blood through the catheter and the insert upon engagement of the insert tip 210 with the valve element 155.

While the examples described herein have focused on inserts having substantially linear insert lumens 260, the insert lumen may be non-linear, and may include branches, etc. Additionally, as shown in FIG. 7, the insert may include one or more outlets at sites other than the distal-most insert tip 210, corresponding to valve membranes having multiple off-set slits.

The phrase “and/or,” as used herein should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts.

Reference throughout this specification to “one example,” “an example,” “one embodiment,” “an embodiment” or “some embodiments” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” “an embodiment” or “some embodiments” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. Any headings provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology.

Certain embodiments of the present invention have described above. It is, however, expressly noted that the present invention is not limited to those embodiments, but rather the intention is that additions and modifications to what was expressly described herein are also included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein were not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations were not made express herein, without departing from the spirit and scope of the invention.

Variations, modifications, and other implementations of what was described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention. As such, the invention is not to be defined only by the preceding illustrative description but by the spirit and scope of the following claims. 

What is claimed is:
 1. A bypass element for a valve, comprising: an insert tip configured to displace one or more edges of a slit in a membrane of a valve without penetrating said membrane; an insert connector adapted to connect to a measurement device; and an insert lumen extending between the insert tip and the insert connector, said insert lumen permitting fluid flow between the tip and the connector.
 2. The bypass element of claim 1, wherein the insert tip has an external diameter sized to fit within a lumen of a valve.
 3. The bypass element of claim 1, further comprising: a proximal insert portion including the connector; a distal insert portion including the tip; a junction between said proximal and distal insert portions; and a compressible element disposed about the circumference of the insert at the junction and configured to permit the insert to compress longitudinally.
 4. The bypass element of claim 3 wherein the proximal and distal insert portions can be rotated relative to one another.
 5. The bypass element of claim 3, further comprising a sealing member disposed at the junction of the proximal and distal insert portions.
 6. A system for bypassing a valved vascular access catheter, comprising: a vascular catheter insertable into a patient; a valve housing in fluid communication with the catheter, the valve housing comprising: a valve lumen and a flexible membrane with a slit therethrough, the membrane being disposed within the valve lumen and the slit remaining closed when a pressure differential thereacross remains below a predetermined threshold; and an insert, comprising: a proximal connector engageable with the catheter; a distal insert tip sized to fit within the valve lumen the valve housing and to open the slit; and an insert lumen extending from the proximal connector to the distal insert tip, the insert lumen configured to permit fluid communication between the proximal connector and the distal tip.
 7. The system of claim 6, wherein the insert further comprises: a proximal insert portion including the proximal connector; a distal insert portion including the distal insert tip; a junction between said proximal and distal insert portions; and a compressible element disposed about the circumference of the insert at the junction and configured to permit the insert to compress about a longitudinal axis when the insert is engaged with a valve membrane.
 8. The system of claim 6, wherein the proximal and distal insert portions can be rotated relative to one another at the junction.
 9. The system of claim 6, further comprising a sealing member disposed at the junction of the proximal and distal housings.
 10. A method of measuring a physical characteristic in a patient having a catheter with a pressure activated valve, the pressure activated valve comprising a membrane having at least one slit therethrough, the slit opening in response to a fluid pressure in excess of a predetermined threshold, the method comprising the steps of: providing a an insert, comprising: a proximal connector engageable with the catheter; a distal insert tip sized to fit within a lumen of the pressure activated valve and open the at least one slit in the membrane without penetrating the at least one slit; and an insert lumen extending from the proximal connector to the distal insert tip, the insert lumen configured to permit fluid communication between the proximal connector and the distal tip; placing the insert into the valve housing and contacting the membrane, thereby permitting fluid transmission between the catheter and the insert lumen; measuring the physical characteristic through the insert lumen.
 11. The method of claim 10, wherein the physical characteristic is selected from the group consisting of a pressure wave, acoustic wave and ECG wave.
 12. The method of claim 10, further comprising the step of determining a position of a distal tip of the catheter based on a measured fluid pressure.
 13. The method of claim 12, further comprising the step of repositioning the distal tip of the catheter.
 14. The method of claim 12, further comprising the step of positioning the distal tip of the catheter in an optimal position.
 15. The method of claim 10, further comprising the step of determining a position of a distal tip of the catheter based on a measured ECG wave.
 16. The method of claim 12, further comprising the step of repositioning the distal tip of the catheter.
 17. The method of claim 12, further comprising the step of positioning the distal tip of the catheter in an optimal position. 